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Domestic Voltage Stabilizer’s Transformer Humming Normalised

By on February 12, 2022
how to fix a broken voltage stabilizer








voltage stabilizer repair

This D V S was on my  bench work with complaint of  loud humming and output voltage showing letter H.  I opened the case and did visual checking. I did observe a bulged e cap, which I did change. When I on the stabilizer, problem same.

bulged e-cap

For your information, when stabilizer shows H at output voltage it means there is high voltage input than what the stabilizer is rated for. So what is the cause of this problem? Got info from Google it may be caused by defective relay, so checked on the relays, all are in good condition.

Checked on other components: e-caps, diode, resistors, transistors, all good. So I decided to do voltage test on the transformer. On transformer it is indicated secondary output voltages.

transformer output voltage

When I did check transformer voltages, to my surprise they were all higher then what  is rated on transformer (300+Voltages) and the voltage primary input to transformer was also more than 300V, (national grid voltage is 220V.)

I guess this is why transformer was humming loudly. So I focus my attention on input voltage circuit. On this circuit, I found two non-polar caps defective: 105/630V and 104/275V.

bad non polar capacitor

bad capacitors

Since I don’t have exact cap, I just replaced the two caps with 105/400V each.

Connect all things together and power On, LOL stabilizer works perfectly. This is the finished repaired work.

how to fix a broken voltage stabilizer

imoudou onwuwah

This article was prepared for you by Imoudu Onwumah from Nigeria. He is 62 years old and has just 3 years experience in electronics repairs. I started career in hotel industry as a chef, but then I was doing repairs only in electrical repairs as a hobbyist. In 2018, I decided to learn about electronics which through Jestine’s electronics e-books and holding my hand, am an electronics techie today.

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Note: You can read his previous article on UNI-T Digital Multimeter Faulty From Time Of Purchase




  1. Parasuraman S

    February 12, 2022 at 9:55 pm

    Good job there! Very professional!

    • Imoudu Onwumah

      February 13, 2022 at 5:57 am

      Hectoring and Tayo,
      Thanks for your comments,I tested almost all components on board.As to non polar cap I tested their capacitance with dmm meter.The yellow cap read 351.6nanofarad,while the red cap read 208.9nanofarad.Both are out of spec.

  2. Albert van Bemmelen

    February 12, 2022 at 10:17 pm

    Good job Imoudu. Sure glad we still do not need those AC stabilizer units on our AC power grid.

  3. Hector De La Torre

    February 12, 2022 at 10:27 pm

    Good job how did you find the bad components non-polarize capacitors?

  4. Steve

    February 12, 2022 at 10:32 pm

    Just wondering how the capacitors were causing to high of a input voltage? Interesting article

  5. Tayo

    February 12, 2022 at 10:35 pm

    Nicely done. How did those filter caps fail exactly? Open, shorted or out of spec?

  6. Erik

    February 12, 2022 at 11:24 pm

    replace capacitar 105/630V for a 105/ 400V; is this ok???? or to low???

  7. Imoudu Onwumah

    February 13, 2022 at 5:22 am

    In my country a/c national grid can suddenly go high or very low,so we use this appliance to stabilise a/c input when it happens.

  8. Raj

    February 14, 2022 at 2:52 pm

    Thanks for sharing. Great job..

  9. Yogesh Panchal

    February 14, 2022 at 11:56 pm

    Good job! Imoudu,
    Try to use exact voltage or Bit Higher Voltage capacitor or chances are high for rework.


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